(Corrects "class" to "group" in 12th paragraph, "women and children" to "families" and "2017 fiscal year" to "2017" in 15th paragraph.)

By Reade Levinson and Kristina Cooke

June 12 (Reuters) - New limitations on asylum imposed by U.S. Attorney General Jeff Sessions could invalidate tens of thousands of pending claims brought by women, children and men fleeing violence in their home countries, according to immigration attorneys.

Sessions on Monday overturned a grant of asylum to a Salvadoran woman whose former husband raped and beat her for 15 years. The decision left immigration lawyers across the United States grappling with how to proceed for their clients.

At least 230,000 of the 711,000 cases before U.S. immigration courts involve asylum petitions from Central America and Mexico, according to a Reuters analysis of data from the Executive Office for Immigration Review, which runs U.S. immigration courts.

Attorneys said most claims from this region are based on domestic or gang violence. Those cases will be far harder - if not impossible - to win in light of Sessions' decision, they said.

In a case known as the "Matter of A-B," the attorney general revoked a ruling by the Board of Immigration Appeals that carved out special protections for domestic violence victims. The decision narrowed who can qualify for asylum because they were victims of criminal activity, as opposed to government persecution.

"Generally, claims by aliens pertaining to domestic violence or gang violence perpetrated by non-governmental actors will not qualify for asylum," the nation's top law enforcement officer wrote.

Sessions' action has left immigration lawyers uncertain about the next steps for their cases.

In Albuquerque, New Mexico, immigration lawyer Rebecca Kitson said she had about six cases pending that were now in doubt.

One involves a teenager whose father, a minister in El Salvador who traveled between gang territories, was gunned down and died in his arms, she said. The gangs then targeted the boy.

"Can't change that they are based on gang violence," Kitson said. "The plan is to keep fighting and hope that appeals and the federal courts will sort it out."

Sessions' decision applies to immigration courts and the Board of Immigration Appeals, which are overseen by the attorney general. Decisions can ultimately be appealed to federal appellate courts, which operate independently, and immigration attorneys say challenges are likely.

Asylum law requires that claims be evaluated on a case-by-case basis. Immigrants fleeing domestic and other violence can still seek relief if they can show their persecution was based on race, religion, nationality, political opinion or membership in a "particular social group." But the ruling narrowed the definition of what that term means.

Previously, for example, some married women who could not leave abusive husbands were considered a "particular social group." But Sessions' decision tossed that definition.

Those with pending cases can amend the basis of their claim while still before an immigration court, though not at the appeals stage. But immigration attorneys say the decision closes off an avenue for relief to some of the most vulnerable immigrants.

At the Dilley, Texas, federal family detention center, the vast majority of the more than 13,000 families served by a legal services project in 2017 were fleeing domestic violence, gang violence or both, according to Royce Murray, policy director at the American Immigration Council. The council is a partner in the project.

In Boston, immigration attorney Matt Cameron said his office has a hearing scheduled on Thursday for a woman who endured years of physical violence from the father of her children. He said the case would have had a strong likelihood of success - before the Sessions decision.

"This person had been through a lot of counseling, a lot of preparation. ... It took a long time to get her to the point where she could actually talk about it," he said. "Now you have to tell them they don't even have a case anymore."

Sessions has vowed to reduce the court backlog, which reached 711,000 pending immigration cases in May. A Department of Justice spokesman said Monday's decision will allow cases "to be more effectively and quickly adjudicated." (Reporting by Reade Levinson in New York and Kristina Cooke in San Francisco; editing by Sue Horton and Jonathan Oatis)

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